Having been a student of the handgun, and especially the revolver, I sort of backed into collecting cartridges. Lately, I've been sorting through and placing them into little Zip-Lok bags and labeling them, according to headstamp, if any, and primer/bullet variations. Over the years I've accumulated quite a variety of specimens.
I have many .45 Colt rounds, old UMC blackpowder, Frankford Arsenal Benet primed, etc. Also some blackpowder .38 Special as well as the .38-44 Special and .38 Special MV, forerunners of the .38 Special +P of today.
I have a few rarities~ the 9.8mm ACP, the .44 Remington and .50 Remington, to name a few.
Makes an interesting study in itself.